Slotted sheet antenna



1957 D. w. PETERSON SLOTTED sEEET ANTENNA Filed Sept. 8, 1953 SLOTTED SHEET ANTENNA Donald W. Peterson, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Deiaware Application September 8, 1953, Serial No. 378,880

7 Claims. (Cl. 343--816) This invention relates to antennas, and particularly to improvements in antennas of the type employing sheet radiators in which the principal radiation or response characteristic is substantially confined to a horizontal plane.

This invention is an improvement over U. S. Patents Nos. 2,480,153 and 2,480,154 issued-August 30, 1949, to Robert W. Masters.

It is an object of this invention to provide a simplified feed system for antennas of the sheet radiator type.

Another object is to extend the length of sheet radiator structure which may be fed from a single feed point in sheet radiator antennas.

These and other objects are achieved, in accordance with the invention, by an antenna structure which utilizes slotted sheet radiators having a continuous outer edge and fed by a feed network at the center of the sheet structure. A half wavelength removed from the feedpoint, the inner portion of the slotted sheet is made discontinuous and a short transposing section is inserted to extend the antenna aperture to another sheet radiator section and to excite this other section with antenna currents of the same phase.

A more detailed description follows in conjunction with the accompanying drawing, wherein:

Figure 1 is an elevation of a sheet radiator antenna structure in accordance with the invention;

Figure 2 is a plan in section along the line 2--2 of Figure 1; and

Figure 3 is a plan view of a turnstile type antenna embodying the invention.

Referring now to Figure 1, there are shown two sheets 11, 13 lying in the same plane on either side of and adjacent a tubular conductive mast 15. Each of the sheets 11, 13 is approximately one wavelength long at the center of the band of frequencies for which the antenna is designed and each of the sheets extends outward radially from the center of the mast 15 a distance of approximately a quarter wavelength at the operating frequency. This sheet radiator structure 11, 13 is coupled to associated radio frequency apparatus by a transmission line,

such as the two-conductor transmission line 17, 19. The feed points for the sheet radiator structure are located at the midpoints of the sheets 11, 13 at their edges nearest the mast 15 and are designated by the reference numerals 21, 23. The transmission line 17, 19 may, ifdesired, be two individual coaxial lines having grounded sheaths and may be located on the exterior of the mast 15 rather than in the interior as shown on the drawing.

At a distance of a half wavelength either side of the feedpoints 21, 23, the sheet radiator structure has a discontinuity in the edge nearest the mast. Extensions 31 of the sheet radiator 11 are also in the same plane adjacent the ends of the sheet 11, and similarly constructed extensions 33 are located in the same plane and adjacent the ends of the sheet 13. The entire sheet structure (considering a single side for example) may be considered a unitary sheet with the outer edges, that is the edge rates Patent C 2,781,513 Patented Feb. 12, 1957 ice farthest removed from the mast 15, continuous throughout and the inner edge nearest the mast 15 having an electrical and spatial discontinuity therein. The feed is extended to the sheet radiator extensions 31 and 33, for example in the lower portion of the drawing in Figure l, by short transposing connections consisting of semi circular conductive straps 35, 37. The strap 35 is connected to the inner edge of the bottom of the main sheet 11 and to the top of the sheet extension 33 that is away from the sheet 11. Similarly, the strap 37 connects the bottom of the oppositely disposed sheet 13 to the top of the oppositely disposed sheet extension 31. Straps 35 and 37 are spaced from the tubular conductive mast 15 and are maintained in insulated relationship therefrom. In the upper portion of the structure shownv in Figure l, straps 39' and 41 form a transposing sec-- tion to extend the feed to the sheet radiator extensions 31. and 33 in the same manner as explained in conjunction; with the straps 35 and 37 immediately above.

The sheet structure is connected to the mast 15 at thetop and bottom by conductive clamping means 43, 45' respectively. If necessary to achieve additional mechani' cal rigidity, sheet radiator structure 11, 13, 31, 33 may be supported at points intermediate the metallic clamping members 43, 45 by suitable insulating members.

Figure 2 is a plan view in section along the line 2-2 of Figure 1 showing the relative disposition of the sheet radiators 11, 13 and the conductive straps 35, 37 which forms the transposing section relative to the mast 15.

The invention may also be used with antennas of the turnstile type to extend the length of aperture which may be fed from a single feedpoint. A plan view of such an arrangement is shown in Figure 3. Four sheet radiators 11, 12, 13 and 14 are shown extending radially from a tubular conductive mast 15. The sheet radiators 11, 12, 13 and 14 are fed in phase progression by known means to provide the required progressive phasing. One suitable connection is described in U. S. Patent 2,086,976, issued July 13, 1937, to George G. Brown.

Four semicircular straps 35, 36, 37 and 38 like the straps 35, 37 shown in detail in Figure 1 are used to form the transposing section. The strap 35 extends the feed from sheet'11 to the extension of sheet 13 and the strap 36 connects the inner edge of sheet 12 to the extension of sheet 14, etc. In each case, the straps 35, 36, 37, 38 connect the inner end of the sheets 11, 12, 13 and 14 to the extension of the sheet located 180 spatial degrees away.

The system of the invention has several important advantages. An aperture as long as two wavelengths at the operating frequency can be fed efficiently from a single feedpoint. The transmission lines which are necessary between the antenna structure and the associated radio frequency apparatus can therefore be simplified due to a reduction of the necessary number of feedpoints, since prior art arrangements required at least two feedpoints to couple the same length of aperture to the associated radio frequency equipment. Furthermore, since the entire length of aperture fed from the single feedpoint in this invention is symmetrically located with respect to the feedpoint, no change of pattern characteristic occurs with change in frequency which would give rise to objectionable scanning of the vertical pattern characteristic.

Multiple layer sheet antennas (like those in accordance with Patent 2,480,154 referred to above) have been constructed with one layer of radiators fed by a transmission line system which gives a difference in phase from the remaining layers of radiators to effect some null fill-in in the vertical pattern characteristic. The same result may be accomplished in accordance with this invention by positioning the plane of one set of sheet extensions 31, 33, for example those in the lower portion of Figure 1 of 3 the drawing, at an angle with respect to the plane of the center portion of the sheets 11, 13.

The sheet radiators used in the invention may be of either solid or perforated structure such screens ,or sheets of parallel conductors. vThe term "fsheet as used in :this specificationandtheappended claims isusedin its ,broad sense as a :current,sheet.and -is intended-to include the conductive sheets and their perforate equivalents.

Whatis claimed is:

1. An antenna system comprising a plurality of conductive sheet elements radially arranged about a conductive supporting member and having an electrically continuous outer edge, the inner edge of said sheets being substantially straight and parallel'to said conductive supporting member, said inner edge being electrically and spatially discontinuous at points removed substantially one-half wavelength at the operating frequency from the center thereof, a transposing connection comprising metallic straps connecting the inner edge of each of said sheets with the inner edge of another of said sheets on the opposite side :ofsaid discontinuous points of said inner edge, and means for connecting transmission line means to the inner edge of said sheets 2. An antenna system comprising a plurality of conductive sheet elements radially arranged about a conductive supporting member and having a Width of substantially one-quarter Wavelength at the operating frequency and having an electrically continuous outer edge, the inner edge of said sheets being substantially straight and parallel to said conductive supporting member but spaced therefrom, said inner edge beingelectrically and spatially discontinuous at points removed substantially one-half wavelength at the operating frequency from the center thereof, a transpos'ing connection comprising metallic straps connecting the inner edge of on of said sheets with the inner edge of another of saidsheets on the opposite side of said discontinuous points of said inner edge, the sheet portions connected by said straps being disposed on opposite sides of said conductive supporting member, and means for connecting transmission line means to the center of the inner edge of said sheets.

3. An antenna system comprising a plurality of conductive sheet elements radially arranged about a conductive supporting member and having a width of substantially one-quarterwavelength at the operating frequency and having an electrically continuous outer edge, the inner edge of said sheets being substantially straight and parallel to said conductive supporting member, said inner edge being electrically and spatially discontinuous at points removed substantially one-half wavelength-at the operating frequency from the center thereof, a transposin'g conn-ection comprising-metallic straps connecting the inner edge ofone of said sheets with the inneredge of another of said sheets on the'oppo'site side of said'discontinuous points of said inner edge, the sheet portions lectrically connected by said straps being disposed on opposite sides of said conductive supporting member, the inner edge of said sheet being electrically connected to said conductive supporting member at the ends thereof, and means for connecting transmission line means to the inner edge of said sheets.

4. An antenna system comprising, an elongated conductive supporting member, first and second elongated conductive sheet having inner edges generally parallel to and spaced from said supporting member, said s'heets being on opposite sides of said supporting member, said inner edges of each of said sheets being provided with a plurality of discontinuities at a given longitudinal distance from the center thereof to form four corners at each adjacent pair of said discontinuities, conductive straps connecting diagonally opposite ones of said corners, and feed means connected to the inner edges of each of said sheets.

5. An antenna system comprising, a vertical hollow mast, a pair of coextensive vertically arranged current sheet radiating elements on opposite sides of and supported by said mast, the inner edges of said sheets'being discontinuous at point on opposite sides of the center of said antenna system, the discontinuity of one sheet being adjacent the corresponding discontinuity of the other coextensive sheet, whereby four corners are formed at each adjacent pair of discontinuities, conductive straps connecting diagonally opposite ones of said corners, and a transmission line passing through the interior of said mast and connected to the inner edges of saidsheets.

'6. An antenna system in accordance with claim 5 wherein said pair of sheets are in the same vertical plane, and there is provided a similar pair of sheets similarly arranged relative to said mast and 'to each other but in a vertical plane at right angles to said first plane and positioned between said first pair of sheets.

7. An antenna system comprising an elongated conductive supporting member, firs-t and second elongated conductive sheets arranged along the length of and mounted on said supporting member, said sheets'beingpositioned 'on opposite sides of said supporting member and having adjacent edges which are provided with a plurality of discontinuitie at a given longitudinal distance firom the center thereof to form four corners at each adjacent pair of said discontinuities, conductive straps connecting diagonally opposite ones of said corners, and feed means connected to said adjacentedges of each of said sheets.

References Cited in the file of this .patent UNITED STATES PATENTS 2,045,987 Green June 30, 1936 2,480,153 Masters Aug. 30, 1949 2,480,154 Masters Aug. .30, 1949 2,558,727 Bernet July 3, 1951 

